- rapidly hydrolyzed --> 6-MAM --> morphine
- both heroin and 6-MAM are more liposoluble than morphine and enter the brain more readily
- morphine and 6-MAM are responsible for pharmacological actions of heroin

Meperidine

- predom miu receptor agonist
- has significant antimuscarinic effects, which may be a contraindication if tachycardia would be a problem
- negative inotropic action on heart
- large doses = tremors, muscle twitches, dilated pupils, hyperactive reflexes, convulsions (b/c of acc of normeperidine which has a half-life of 15-20 hrs compared to 3 hrs for meperidine)
- decreased renal or hepatic fxn increases likelihood of toxicity

Meperidine - Drug Interactions

Serotonin syndrome - delirium, hyperthermia, headache, rigidity, convulsions, coma, death
- rxn may be due to ability of meperidine to block neuronal reuptake of serotonin and resulting serotonergic overactivity
- so meperidine should NOT be used in pts taking other serotonergic agents such as MAOI

- care should be taken not to administer any partial agonist or drug w/ mixed opioid receptor actions to pts receiving pure agonist drugs b/c of the unpredictability of both drugs' effects: reduction of analgesia or precipitation of an explosive abstinence syndrome can result

Opioid Antagonists

Naloxone, Naltrexone, and Nalmefene

Naloxone, Naltrexone, and Nalmefene

- high affinity for miu receptors
- lower afffinity for kappa and delta but can reverse the action of agonists at kappa and delta receptors
- Naloxone = tx of acute opioid overdose
- Naltrexone = long duration of action so is proposed as maint drug for addicts in tx programs
- Naltrexone decreases craving for alcohol in chronic alcoholics

Antitussives

- opioid analgesic --> suppression of cough
- different receptors than those assoc with other actions of opioids
- Dextrometorphan, codeine, levopropoxyphene, noscapine
- should be used w/ caution in pts taking MAOIs

Dextrometorphan

Codeine

Levopropoxyphene

Dextrometorphan - dextro isomer of a derivative of levorphanol

Codeine - useful antitussive at doses lower than those required for analgesia